I've posted about my intermittent MAF sensor elsewhere but am wondering about what symptoms people are experiencing with a dirty or failing MAF sensor.

My 2004 was idling high, swinging from 1500 to 3000 RPM. Sitting at a light it'll be racing and revving making me look like a jerk. It'll idle down the road at 40 MPH. Braking and slowing will bring the idle speed down.

The only reason I suspected the MAF is that when this happened many months ago, the CEL came on and an auto parts store told me it was a MAF code (don't know which one).

The problem immediately went away for months.

After the problem came back a few weeks ago, I cleaned it with MAF cleaner and it immediately ran better.

Today it was revving higher and wilder than ever.

I'm planning to the MAF sensor tomorrow - BUT, I can't find a single description of MAF sensor problems that is similar to my symptoms.

Anybody else with this rev problem due to a MAF sensor?

 

Could possibly be the TPS inside the throttle body too.
You can remove the black plastic cover and spray the contact fingers and the runs on the circuit board with contact cleaner.
( NOTE: If you plan on removing the throttle body for this, get a new O ring before you do. )
Are you sure it's not just a vacuum leak ?

 

Thanks for the suggestions. I'll look into the TPS as a possible problem too (good tip on the O-ring).

From what I've read about TPS problems, the engine typically will hesitate when the accelerator is pressed. When I blip the throttle or accelerate quickly, the engine responds immediately.

Also, re. a vacuum leak, it doesn't stall and doesn't hesitate when I mash the throttle - both of which are symptoms of a vacuum leak, right? I can't detect any hissing sounds either.

When I drove it this morning, it's revving even higher and I had to turn off the engine when stopped at lights.

 

ala_xfire,

I can't locate a TB o-ring locally so I'm going to just clean the TPS connector at the TB. Can you give me some tips on removing that? Spent 15 minutes on it without luck.

Also read threads on vacuum leaks. I can't hear anything obvious. Can you suggest some locations that are more typical?

Thanks.

PS This guy had what sounds like the same problem but didn't post a resolution: https://www.crossfireforum.org/forum...ssue-help.html

 

The CPS is a pain because it's tight down there. The issue is a little lip which holds the clip to the sensor. You have to carefully pry that little plastic clip up so when you pull on the connector to unplug it, it will indeed be able to be pulled off of the CPS.

As far as vacumn lines, I'd just say check everywhere. If you've had / or done any service recently it could be it wiggled off or was never reattached. There's one that goes down to the TB area that may have been pulled off or cracked. Also, if you've been messing with the CPS, there's one that connects to the top of the engine that could have been pulled off.

Good luck.

 

The sage continues...

I used the propane torch and tube method to search for vacuum leaks but didn't find anything.

I cleaned the MAF sensor with MAF cleaner and it worked!!... for a few weeks.

I replaced the MAF sensor assembly and it worked!!... for a few weeks.

The oscillating idle speed and idle-down-the-road-at-40mph problems started again a few days ago. This morning I decided I'd take it into my independent Mercedes shop tomorrow to let them sort it out.

But the next time I started my car this afternoon, it was fine again.

I don't think it's a throttle position problem since the when the engine is revving up and down when I'm not moving, the engine is bouncy and rough. If I was just revving up and down with my foot, it would be smooth. Also, when I'm driving, it doesn't idle up and down but only idles high.

Any new ideas? It's driving me batty!

 

Just a thought but if the CPS, wouldn't the tach be jumping around ?


Nice thing about Torque Pro is that is can display/log a lot of parameters (engine was off when picture was taken).

 

When my crankshaft position sensor failed, the engine wouldn't start at all. But, there may be other failure modes.

For $5 plus a bluetooth OBD2 adapter, the Torque Pro is probably worth a shot.

 

It has been stated that unscrewing the bolt holding the CPS in place and then releasing the latch is the best way to do this job.

 

X-fired, any chance you were able to resolve this issue? I currently have had this issue with mine and have been unable to fix it. I have a 74 mm TB upgrade and a CAI i installed both a year ago. This randomly started happening. I tried changing the pedal assembly (No fix), just replaced the whole breather assembly (Still no fix), Cleaned the MAF sensor and TB (No fix) Just ordered a new MAF sensor, and will try that. I am 100% sure I have no vacuum leaks. I have the same symptoms as you.

 

The 74mm MAF body runs best when using the sensor from the smaller MAF body.
Others have run with the larger sensor but not too many.

 

Yes, it turns out it was the throttle body. I replaced it with a used one from a member on this forum and the problems went away.

 

I am using a 74 MM throttle body with a needswing MAF Elbow with the OEM MAF Sensor.

 

Did you replace (or set correctly) the 'O' ring at the intake/Throttle body? If not in its 'slot', you will have a vac leak and erratic idle.


.

 

I did seat it 100% right, I just went back out and did a quick check and it looks look. Im hoping it is the maf sensor, or at least the TB is bad. This isn't something that happened after i changed parts. This happened out of the blue.

 

Great, one down who knows how many more. If you take it one step at a time, it'll come to you. Since you did check for any vac leaks, I will take it you used something besides visually checking each hose?


.

 

yes, I replaced all the breather hoses, the T, and the line going to the trans

 

Did you check for any codes through your OBD port? How about gas, did you refill gas a couple times at a different gas station?


.

 

no codes, I’m not sure about gas, because this issue comes and goes, sometimes it is fine (25%) other times sporadic idle and high idle (75%) this started about 3 weeks ago. New maf sensor getting delivered today.

 

Have you inspected the doughnut gasket between the engine cover and the MAF body for damage?
These get damaged easily.